Pulse rate monitor and indicator system utilizing a burst pulse counter and a pulse internal counter

ABSTRACT

A receiver apparatus adapted to have coupled thereto intentionally transmitted signals, each being characterized as having a predetermined number of pulsations, which are transmitted over a communication link such as the standard switched telephone network and, at times, noise signals which are introduced into the communication link. The receiver includes measuring means arranged to measure the time interval between successive signals coupled thereto, and signal verification means to verify that each signal coupled to the receiver is either an intentionally transmitted signal or a noise signal. In the event that a noise signal is coupled to the receiver, the signal verification means is arranged to abort measurements of the measuring means. Measurements not aborted are indicative of the time interval between each two successive intentionally transmitted signals coupled to the receiver.

United States Patent Malchman et a1.

1541 PULSE RATE MONITOR AND INDICATOR SYSTEM UTILIZING A BURST PULSECOUNTER AND A PULSE INTERNAL COUNTER [72] Inventors: Franklin L.Malchman, Montgomery; William J. Raddi, Philadelphia, both of Pa.

[73] Assignee: ESB Incorporated [22] Filed: April 2, 1971 [21] Appl.No.: 130,632

[52] US. Cl ..340/171 R, 235/92 CC, 307/234,

[51] Int. Cl. ..G06m 01/00, 1-103k 05/20- [58] Field of Search..328/109, 110, 119; 307/232,

307/233, 234; 340/171, 167, 167 A, 168, 164, 206; 325/324, 325; 329/107,126; 235/92 CC [56] References Cited UNITED STATES PATENTS 3,586,8356/1971 Foeh, Jr. ..235/92 CC 3,601,706 8/1971 Battle, Jr. ..307/234 X3,185,963 5/1965 Peterson et a1. ..340/168 R 3,518,555 6/1970Konotchick, Jr. .....307/232 X 51 Aug. 22, 1972 OTHER PUBLICATIONS IBMTechnical Disclosure Bulletin, Vol. 6, No. 7, December 1963, pg. 74, 75Variable Frequency Missing Pulse Detector R. L. Adams, Jr.

Primary Examiner-Donald J. Yusko Att0mey-Robert H. Robinson, Raymond L.Balfour, Anthony J. Rossi and Thomas A. Lennox ABSTRACT A receiverapparatus adapted to have coupled thereto intentionally transmittedsignals, each being characterized as having a predetermined number ofpulsations, which are transmitted over a communication link such as thestandard switched telephone network and, at times, noise signals whichare introduced into the communication link. The receiver includesmeasuring means arranged to measure the time interval between successivesignals coupled thereto, and signal verification means to verify thateach signal coupled to the receiver is either an intentionallytransmitted signal or a noise signal. In the event that a noise signalis coupled to the receiver, the signal verification means is arranged toabort measurements of the measuring means. Measurements not aborted areindicative of the time interval between each two successiveintentionally transmitted signals coupled to the receiver.

9 Claims, 2 Drawing Figures W 7l sfi ii fi FL 1P- F P l8 NETWORK R LOMULTIVIBRATOR T CONTROL FLIP- FLOP AND CLOCK GATE INTERVAL COUNTER RESETBURST PULSE COUNTER DECODE 3O STB-2 STROBE 1 GENERATOR 80 STE 1 BURST 98DECISION o FLIP-FLOP R J l 32 STORAGE REGISTER READOUT DISPLAY PULSERATE MONITOR AND INDICATOR SYSTEM UTILIZING A BURST PULSE COUNTERANDAPULSEINTERNALCO BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to receiver apparatus. Moreparticularly, the invention concerns novel receiver apparatus which mayform a part of a monitor apparatus which in turn, can be used to provideinformation or indicate to an observer, and/or record the state orcondition of the power supply, generally comprising a battery, supplyingelectrical energy to an organ stimulator; such information or indicationbeing derived from the rate of operation of the organ stimulator.

2. Description of the Prior Art By the way of background, it may beexplained that electronic heart pacers are used in the treatment ofheart block. Simply stated, heart block occurs when the natural periodicelectric stimulation signals generated on a portion of the heart, theatrium, are for some reason partially or wholly blocked or preventedfrom reaching another portion of the heart, the ventricle. Because ofthe blockage, the ventricle does not function, at all if the block iscomplete, or pump at the proper time or at the proper rate if the blockis partial.

Essentially, an electronic heart pacer is a device used to overcome ortreat heart block. In recent times, the electronic pacers have beenminiaturized and are now wholly implanted within the body, usually justbelow the level of the skin. Implanted pacers are usually selfcontainedand powered by battery. The pacers generate electric stimulation pulseswhich are then applied via a flexible lead or leads, to the heart. Thegenerated electric pulses, i.e., artificial stimulation signals, whenapplied to the heart, simulate the natural periodic electric stimulationsignals generated on the atrium and result in the ventricle pumping atthe proper time and rate as in normal situations. Generally, the heartis electrically stimulated to beat once for each pulse that is generatedby the pacer and received at the heart.

There are three broad categories into which most commercial pacers fall,namely, the synchronous types, the asynchronous types and the inhibitedor standby types. The synchronous types are also sometimes referred toas triggered pacers in that their operation is effected by a signalderived from body activity which is sensed and fed back to the pacer totrigger its operation; the derived trigger signal usually being thepresence or absence of either atrial or ventricular activity. Theasynchronous types are also sometimes referred to as non-triggered inthat they do not respond in any way to body activity; they operate at afixed rate. The inhibited or standby types under normal cardiac activitydo not produce stimulation pulses, however, if spontaneous rhythm is notsensed within a predetermined time interval, as for example, 1 second,then the pacer delivers a stimulating pulse, and continues to deliverpulses until normal heart rhythm is restored.

Most triggered pacers and most inhibited or standby pacers contain amagnetic switch which can be externally activated to convert the pacerto asynchronous or non-triggered operation.

As stated above, pacers are usually powered by batteries. The batteriesbest suited for powering pacers normally maintain a substantiallyconstant voltage throughout their lives, and then, near the end of theirlives run down over a relatively short period of time. Generally, towardthe end of life of the batteries of a pacer operating, or caused tooperate in a non-triggered mode, the pulse rate thereof decreases (theoutput pulse interval increases) and consequently, the heart beatsslower. There is a type of pacer, however, in which the pulse rateincreases with a decrease in battery voltage. In addition to changes inpulse rate due to battery exhaustion, a pacers pulse rate may change dueto physiological conditions or due to malfunction of conditions pacer.

It is, of course, important that changes in the pulse rate of a pacer,after implant, be detected at the earliest possible time in order thatthe cardiologist treating the patient may take appropriate measures tosafeguard the life of the patient, as for example, he may consider thatreplacement of the pacer is called for when the pulse rate of the pacerfalls to some predetermined rate or departs significantly up or downfrom the rate determined or set at the time of implantation.

From the foregoing, it will be understood that an indication of thecondition or state of the power supply or battery of a pacer operating,or caused to operate, in a non-triggered mode may be had by determiningthe time interval between two successive pulses of the pacer.Consequently, it has become desirable to provide an apparatus that wouldmonitor the pulse rate of a pacer and as the pulse interval of the pacerchanges, due to a defective battery, or the critical period of rapiddecline in battery voltage near the end of its life, or for any otherreason, to give an indication of such a change in pulse interval. Suchan apparatus would provide the cardiologist with an effective means tomonitor and ascertain the performance or condition of the battery orbatteries of the pacer. Even more desirable would be apparatus that canbe adapted to perform such functions from outside the body and from aremote location in order that it not be required that the patient makefrequent trips to the office of the cardiologist.

Such apparatus has in fact been recently developed. See the abstractentitled Transtelephone Pacemaker Clinic by S. Furman, B. Parker, and D.Escher, published in the American Journal of Cardiology, Volume 25, page94. The abstract cited does not go into details of the apparatus usedfor the monitoring of a patients implanted heart pacer via telephonelines, however, the apparatus used is known to the present inventorsandcomprises a transducer situated with the patient, usually in hishome, and a receiver coupled to an electronic interval counter locatedat some central office, laboratory or hospital. Each pacer output pulseis detected or sensed by the transducer at the patients hands andconverted to an audible signal which is acoustically coupled to thepatients telephone handset for transmission to another telephone handsetat the receiver location; The received audible signals are converted toshort electrical pulses by the receiver and the receiver delivers theseelectrical output pulses to the electronic counter. The counter isadapted to provide a display of the time interval, in milliseconds (ms),between received signals. The time interval between received signalsprovides an indication to an observer or personnel at the receiverlocation of the voltage state of the batteries of the pacer beingmonitored. More particularly, the time between received signals iscompared to previously received or recorded data compiled over a periodof time and the degree of change is then used as an indication of thestate of the batteries of the pacer. The received data may, of course,be used for other diagnostic purposes.

In the prior art apparatus just described, the sensed pacer outputpulses were converted by the transducer to audible signals which may becharacterized as short bursts of sound or clicks. These clicks were thentransmitted overthe standard telephone network to the receiver location.At the receiver location, the time interval between clicks was thenmeasured by an interval counter. At times, telephone line noise maskedthese clicks, interfered with the measurements, and produced erraticresults so that a considerable amount of practical judgment was requiredon the part of the operator, located at the receiver location, to obtainconsistent and reliable readings. Often, a reading was obtained onlybecause the operator had some prior knowledge of the value of timeinterval to be measured. At times, due to telephone line noise, it wasimpossible to obtain any reading whatsoever. Manipulating gain controlson the receiver could only partially mitigate the effects of telephoneline noise. Again, operator experience was required to properly adjustthese gain controls as well as the various controls of the intervalcounter.

Another problem in the prior art monitor apparatus described wasmanifested in the transducer used to sense the pacer output pulses. Thetransducer was susceptible 'to ambient electrical fields such asproduced by fluorescent lights, electric razors, DC electric motors, oreven the proximity of a 60 cycle current carrying wire. Thissusceptibility resulted in the introduction of spurious clicks onto thetelephone line, a situation which is completely intolerable for accuratetime interval measurements of the type described.

SUMMARY OF THE INVENTION Many of the problems associated with the priorart monitor apparatus described have been eliminated by modifying themonitor apparatus and adapting the transducer of the monitor apparatusto convert the sensed pacer pulses to audible tone bursts ofpredetermined frequency and duration. The reader is referred to acopending application Ser. No. 118,144filed Feb. 23, 197i, assigned tothe assignee of the instant application wherein a more completedescription of a monitor apparatus and the novel transducer thereof isset forth. For the present discussion, however, it is only necessary tounderstand that with each pacer output pulse the transducer disclosed inthe referred to application emits, not a click, but a tone burst,approximately 50 ms in duration and with a frequency of ZKl-lz,hereinafter sometimes referred to as an intentionally transmitted toneburst signal, and that the novel receiver, in accordance with thepresent invention, derives valid time interval information between theleading edges of each such two successive tone bursts and rejectsinterference by impulse noise.

Briefly, there is provided by the present invention a receiver apparatusadapted to have coupled thereto intentionally transmitted signals, eachbeing characterized as having a predetermined number of pulsations,which are transmitted over a communication link, and, at times, noisesignals which are introduced into the communication link. The receiveris constructed and arranged to continually sift through all signalscoupled thereto to locate each two successive intentionally transmittedsignals without any intervening noise signals therebetween for providinginformation indicative of the time interval between each such twosuccessive intentionally transmitted signals.

A more complete understanding of the invention will be had from thefollowing detailed description taken in connection with the accompanyingdrawings which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of thereceiver in accordance with the invention; and

FIG. 2 is a timing diagram useful to explain the operation of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to lay a foundation ofthe detailed description of the operation of the receiver of theinvention which follows hereinafter, a brief description of the generaloperation of the receiver will first be given, and this will be followedby a brief description of the interconnection of the various componentsof the receiver. In the latter description, a partial outline of thefunctions of certain of the components of the receiver will be setforth. The functions of the various components not given in this outlinewill, however, become evident or appear in the detailed description ofthe operation of the receiver.

General Description of Operation It may be further explained here thatthe receiver of the invention was developed for use in monitor apparatusadapted to monitor electrical stimulation signals due to either naturalor artificial electrical stimulation of a body part via a communicationlink such that the repetition rate of the electrical stimulation signalscould be determined. More specifically the receiver of the invention wasdeveloped for use in conjunction with the novel transducer means setforth and claimed in the above identified copending application. Thatnovel transducer means, when sensing the output pulses of a cardiacpacer, as for example, emits, not a click, but a tone burst,approximately 50 ms in duration and with a frequency of ZKHZ, for eachpacer output pulse. The tone bursts are each transmitted over thestandard switched telephone network. it is the function of the receiverof the invention to process the received signals and provide informationto an observer indicative of the pulse repetition rate of the cardiacpacer whose output pulses are being monitored. More specifically, thereceiver of the invention is adapted to have coupled thereto audiblesignals which are transmitted over a telephone communication link, theaudible signals including intentionally transmitted audible signals,i.e., tone bursts approximately 50 ms in duration with a ZKHz frequency,and at times, audible noise signals which are introduced into thecommunication link. The receiver of the invention is constructed andarranged to continually sift through all signals coupled thereto tolocate each two successive intentionally transmitted signals without anyintervening noise signals therebetween for providing informationindicative of the time interval between each such two successiveintentionally transmitted signals and, therefore, provide informationindicative of the pulse repetition rate of the cardiac pacer beingmonitored.

The receiver accomplishes this by means of unique digital techniques.The receiver of this invention derives valid time interval informationbetween the leading edges of two successive intentionally transmittedtone burst signals and rejects interference by impulse noise, i.e.,non-intentionally transmitted and/or received signals. As for example,when a first signal is received, detection, by the receiver, of theleading edge thereof initiates a time interval measuring process andsimultaneously initiates a verification or recognition measurementprocess to recognize whether or not an intentionally transrnitted toneburst signal has been received. If the recognition process is positive,the receiver continues with the time interval measuring process. Theleading edge of the next or a second received signal stops the timeinterval measuring process and begins a second recognition measurementprocess. If the second recognition measurement process verifies that thenext or second received signal is in fact an intentionally transmittedtone burst signal, then the results of the time interval measuringprocess are displayed. The displayed information may, for example, takethe form of the time in milliseconds between the leading edges of thetwo successive received signals or may be a direct reading of the rateper minute of the received signals.

If however, the second received signal is a noise impulse, the timeinterval measurement process would again cease, but the secondrecognition measurement process would not verify that a tone burst hadbeen received. In this situation, the time interval measurement processwould be aborted and not displayed. The results of any previous validtime interval measurement would, however, remain displayed.

Ifthe first signal were a noise impulse, the time interval measurementprocess would have been aborted at the conclusion of the firstrecognition measurement process.

The receiver, accordingly, continually sifts through all receivedsignals to fine two consecutive intentionally transmitted tone burstsignals without intervening noise impulses to perform a valid timeinterval measurement and automatically rejects time intervalmeasurements arising from any other combination of signals.

Interconnection of the Various Components In the following descriptionvarious logic elements are described described. AND and OR gates arewell known in the art. An AND gate yields a logic one (1) on its outputterminal if all of the input terminals thereof have logic ones appliedthereto; a logic zero (0) appears on its output terminal if a logic 0appears on any of its input terminals. An OR gate yields a logic 1 onits output terminal if a logic 1 is applied to any of its inputterminals; a logic 0 appears on its output terminal if all of its inputterminals have logic zeros applied thereto. In addition, a number ofbistable devices (flipflops) are employed in the receiver of theinvention. The two possible states of the various bistable devices maybe represented on the output terminals of the bistable devices as logicones and zeroes. Depending on the type of bistable device, a signal onits input terminal may or may not change the state of the bistabledevice; this will be indicated in the description of each bistabledevice. In both the AND and OR gates and in the bistable devices, groundstates usually represent logical zeroes and voltage levels usuallyrepresent logical ones.

Referring now to FIG. 1, the receiver in accordance with the inventionis shown generally at 10. A signal pick-up means is shown at 12. Thesignal pick-up 12 is operatively connected to an Amplifier 14. TheSignal pic 12 is adapted to be placed adjacent to the earpiece containedin the handset of a standard telephone. Preferably, the Signal Pick-up12 comprises a magnetic type such that the variations in current whichdrive the telephone earpiece are magnetically coupled to the Amplifier14. If desired, the Amplifier 14 may be acoustically coupled to thetelephone earpiece via a microphone. The signals appearing on the inputterminal 17 of the Amplifier 12 may be generally characterized asapproximate sine waves. That is, they are signals varying about a DCreference level; see line of FIG. 2. Pick-up The Amplifier 14 hassufficient gain to accommodate most attenuation looses that can beexpected on standard switched telephone network. That is, the Amplifierhas sufficient gain to trip the Threshold Network 16 which is connectedto the Amplifier 14. The signals appearing on the input terminal 18 ofthe Threshold Network 16 are substantially identical to those appearingon the input terminal 17 of the Amplifier 14, the level of the signalsis, of course, higher; see line 102 of FIG. 2

The Threshold Network 16 is essentially a device to convert the signalsappearing on its input terminal 18 into a standardized pulse train ofsignals; see line 104 of FIG. 2. The Threshold Network 16 may, forexample,

comprise a Schmitt trigger circuit or any other suitable thresholddevice.

Signals emanating from the Threshold Network 16 appear at point 20 andare fed to two components of the receiver 10, namely, the Mono-Controlflip-flop 22 and the Burst Pulse Counter 24. The flip-flop 22 is aset-reset type. It sets on the reception of the first pulse or signalemanating from the Threshold Network 16 and no further signals effect ituntil it is reset by the application of a signal on its reset terminalR. Accordingly, its function in the receiver 10 is to provide a signalon its output terminal 26 when the first signal of a train of signalsfrom the threshold network 16 ap pears on its set or S terminal.

The Burst Pulse Counter 24 is a digital counter adapted to count thenumber of pulses in the trains of standardized pulses emanating from theThreshold Network, and, as will be explained more carefully hereinafter,after a predetermined count has been achieved, provide output signalsvia trunk line 28 to a counter Decode device 30. The Burst Pulse Counter24 essentially performs the recognition or verification measuringprocess as will be explained more fully below.

The Decode device 30 essentially is a multiple input AND gate followedby an inverter constructed and arranged to provide an output decodesignal when the Burst Pulse Counter 24 reaches the predetermined countprogrammed therein and applied the required input signals via trunk line28 to the input side of the Decode device.

The output of the Decode device 30 is connected to the set terminal S ofthe Burst Decision flip-flop 32. The flip-flop 32 is the type that isset on the application of signals on its set terminal S and is reset onthe application of a signal on its reset terminal R. The output terminal34 of the flip-flop 32 is connected to the input terminal 36 of ANDReset Gate I. The output terminal 38 of the flip-flop 32 is connected tothe input terminal 40 of the AND Transfer Gate 42. The output terminal44 of gate 42 is connected to an input terminal 46 of the StorageRegister and Readout Display device 50.

The AND Reset Gate I will provide an output signal on its outputterminal 52 when both of its input terminal 36, 54 have the proper inputsignals applied thereto. The output signal at terminal 52 is applied toan input terminal 56 of the OR gate 58 and to the reset terminal R ofthe Clock On-Oif Control flip-flop 60. The output terminal 62 of the ORgate is connected to the reset terminal of an Interval counter 64. Theother input terminal 63 of OR gate 58 is connected to the outputterminal 65 of an AND Reset Gate II.

The Clock On-Ofl Control flip-flop 60 is the type that toggles from oneof its states to the other upon the application of a signal to its inputterminal T. It can also be reset by the application of a signal to itsreset terminal. The output terminal 67 of flip-flop 66 is connected tothe input terminal 69 of AND clock gate 66. The output terminal 68 offlip-flop 60 is connected to an input terminal 70 of AND Reset Gate Hand to an input terminal 72 of the Transfer Gate 42. The input terminal74 of AND clock gate 66 is connected to a IOKHz Pulse Oscillator 76sometimes hereinafter referred to as Clock 76.

The Pulse Oscillator 76 is the basic timing device of the receiver andis a pulse generator for providing a continuous pulsating signal at apreselected KHz frequency to the input terminal 74 of the AND Clock Gate66. With the proper signal applied to input terminal 69 of the AND ClockGate 66, the Pulse Oscillator 76 will deliver a precise train of IOKl-Izpulses, via lead 71 to the Interval Counter 64 which is a digitalcounter adapted to count the pulses. When an output signal appears onthe output terminal 44 of the AND Transfer Gate 42, the information orcount in the Interval Counter 64 will be transferred to the StorageRegister and Readout Display 56 via trunk line 98. The remainingfunctional components of the receiver 10 comprise the Process DelayMonostabie Multivibrator 78 and the Strobe Generator 80.

As will become more apparent hereinafter, the ultimate function of theProcess Delay Monostable Multivibrator 78, in the over-all scheme of thereceiver, is to provide a delay in the measuring process performed bythe receiver to allow sufficient time for the Burst Pulse Counter 24 toperform its verification or recognition measurement process. The outputterminal 82 of the Process Delay Monostable Multivibrator 78 isconnected to the input terminal T of the flip-flop 6t and the inputterminal 84 of the Strobe Generator 80. The

Strobe Generator has two output terminals STB-1 and STE-2. The terminalSTB-l is connected to the input terminal 54 of AND Reset Gate I and toan input terminal of the Transfer Gate 42. The terminal STE-2 isconnected to the input terminal 92 of AND Reset Gate II and to the resetterminals of flip-flop 22, Burst Pulse Counter 24 and flip-flop 32.

Detailed Operation The detailed operation of the receiver of theinvention may best be understood by reference to FIG. 2. In FIG. 2, thewaveforms shown on line represent the signals at point 17. Thesewaveforms are the output signals of the Signal Pick-up 12 and the inputsignals to the Amplifier 14. In case A, wherein two successive tonebursts are received, each waveform generally represents a signalcharacterized as having a predetermined number of pulsations and,specifically, in this example, each represents a ZKHZ signal with a 50ms duration. These would be representative of two intentionallytransmitted audible signals transmitted over the telephone network andcorrespond to two successive output pulses of an implanted cardiacpacer. The time interval measured in case A represents a valid timeinterval measurement and is measured between the leading edges of thetwo waveforms. In case B, wherein a noise impulse is received, thewaveform on line 100 represents such a noise impulse; as can be seen,the duration of the noise pulse is less than 50 ms in duration. In caseC, on line 106 there is depicted a situation wherein an intentionallytransmitted audible signal has been received corresponding to a paceroutput pulse, and this is followed by a noise pulse. The time intervalmeasured in case C represents an invalid time interval measurement asmeasured between the leading edges of the two waveforms. The linesdesignated 162 through 136 essentially represent timing diagrams for thevarious outputs of the components of the receiver 10 and those outputsthat are indicated are labeled at the left-hand margin of FIG. 3. Itwill be noted that only waveforms of the output of one of the terminalsin each of the flip-flops is shown, it being understood that otherterminals of each flip-flop is the opposite to that depicted at anygiven time. As for example, in line 112, at time t when the outputterminal 67 is at a logic 1 level, the terminal 68 would be at groundlevel or logic 0.

Considering case A in FIG. 3, at time t and beginning at line 104 withthe standardized train of output pulse signals from the ThresholdNetwork 16, the first pulse from the Threshold Network initiates twosimultaneous processes. Parenthetically, the leading edge of his firstpulse from the Threshold Network corresponds to the leading edge of areceived intentionally transmitted tone burst. The first process is atime interval measurement process, and the second process is averification or recognition measurement process. The first or timeinterval measurement process ceases with the reception of the nextsignal applied to the receiver and, in case A, the next signal receivedis another intentionally transmitted tone burst. The second orrecognition measurement process essentially measures the duration ofeach received signal.

Beginning with the first measurement process, the first pulse from theThreshold Network 16, at time t sets the Mono-Control flip-flop 22 (line166 resulting in a logic signal appearing on its output terminal 26 andthis logic 0 signal is applied to the Process Delay MonostableMultivibrator 78. With the application of the logic 0 signal to theProcess Delay Monostable Multivibrator 78, the Monostable Multivibrator78 is tripped to provide a logic 0 signal (line 108) at point 82. Thelogic 0 signal at point 82 has no effect on the Strobe Generator 80 butdoes cause the Clock On-Off Control flip-flop 60 to toggle resulting ina logic 1 signal (line 112) to appear on its output terminal 67 and alogic 0 signal to appear on its output terminal 68. The logic 1 signalon output terminal 67 is applied to input terminal 69 of AND Clock Gate66 thus enabling Clock Gate 66 (line 114). Accordingly, the Clock gate66 permits the lOKI-Iz Pulse Oscillator 76 (line 110) to beginregistering a time interval in the Interval Counter 64, that is, theInterval Counter 64 beings to count the number of pulses passing throughthe Clock Gate 66. This counting of pulses from the Pulse Oscillator 76continues until Clock Gate 66 is disabled.

As stated above, the second or recognition measurement process alsobegins with the first 'pulse from the Threshold Network. Beginning attime t the first pulse and the succeeding pulses from the ThresholdNetwork 16 (line 104) are applied to the Burst Pulse Counter 24. Eachpulse in the train of pulses from the Threshold Network 16 is counted bythe Burst Pulse Counter 24. If the counter 24 achieves a predeterminedcount which can be equated to a 50 ms interval, which it will in thecurrent example as the first waveform received is in fact 50 ms induration, then it provides appropriate output signals to the Decode unit30 via trunk line 28 to cause the output of the Decode unit 30 toprovide a logic 0 signal (line 116), at time t to the set or S terminalof the Burst Decision flip-flop 32. When the Decode unit provides anoutput decode signal, the recognition measurement process in effectverifies that an intentionally transmitted tone burst has been received.A logic 0 signal on the S terminal of flip-flop 32 will cause it to setresulting in a logic 1 signal (line 118) at time t to appear on itsoutput terminal 38 and a logic 0 signal to appear on its output terminal34. In this condition, the flip-flop 32 applies a logic 1 signal to theinput terminal 40 of the AND Transfer Gate 42 and a logic 0 signal tothe input terminal 36 of AND Reset Gate 1 These latter two gates are notenabled at this time due to the logic 0 signal appearing on the inputterminal 36 of AND Gate I and due to the logic 0 signal provided byflip-flop 60 on its output terminal 68 which also appears on the inputterminal 72 of the Transfer Gate 42. At time t line 166, the ProcessDelay Monostable Multivibrator 78 times out resulting in a logic 1signal appearing at point 22. It may be pointed out here that theProcess Delay Monostable Multivibrator, when first activated remains inthe condition such that it provides a logic 0 signal at point 82 for apredetermined length of time. Typically, this time delay may beapproximately 80 ms when processing tone bursts 50 ms in duration. Thisdelay, however, is arbitary and may be set depending upon otherconsiderations such as the required time for the Burst Pulse Counter toperform the recognition measurement process. It may also be point outthat while tone bursts of ZKHz with a 50 ms duration have been used inthe examples herein, other tone bursts of different frequencies and ofdifferent duration may be transmitted to the receiver 10 and thereceiver 10 may be adapted to process them in like manner to theexamples given herein. As for example, 4Kl-Iz tone burst signals 25 msin duration may be intentionally transmitted over the conununicationlink and be coupled to the receiver 10; in this case, with eachsuccessive signal coupled to the receive 10, the Burst Pulse Counter 24will achieve the predetermined count of 100 as it would with anintentionally transmitted 2Kl-lz tone burst signal 50 ms in duration.From the foregoing, it will be understood that the signal verificationprocess requires only that each of the intentionally transmitted signalsbeing coupled to the receiver 10 have a predetermined number ofpulsations and that the number of these pulsations be counted by theBurst Pulse Counter 24 which, after a predetermined count has beenachieved, will provide an output signal to the Decode unit 30. Inaddition, it may be pointed out that the receiver 10 may also beconstructed and arranged to be frequency selective so that only onepreselected frequency having the proper number of pulsations will beaccepted by the receiver 10. This may be accomplished by incorporating anarrow pass band frequency selective filter in the amplifier 14whichwould pass signals only of the preselected frequency and reject allother. In this manner, the signal verification process will only processintentionally transmitted signals of the preselected frequency.

At time t the transition of the Monostable Multivibrator 78 from a logic0 level to a logic 1 level causes the Strobe Generator 80 to provide astrobe pulse or logic 1 signal (line 120) on its output terminal STB-1.This logic 1 signal is applied to the input terminal 54 of Reset Gate 1with no effect due to the logic 0 signal appearing on its other inputterminal 36, and to input terminal of Transfer Gate 42 also with noeffect due to the logic 0 signal appearing on its input ter minal 72.

Because the Transfer Gate 42 is not enabled, the signal on its outputterminal 44 at time t, is a logic 0. Thus, not transfer of data takesplace at time t nor is the lnterval Counter reset.

After the first strobe pulse disappears, and after some arbitary shortperiod of time, as for example 10 to microseconds, a second strobe pulseis generated by the Strobe Generator 80 which appears on its outputterminal STE-2 as a logic 1 signal (line 122 at t,,). The logic 1 signalon terminal STE-2 is applied to the input terminal P2 of AND Reset GateII with no effect due to the logic 0 signal appearing on its other inputterminal 71); to the reset terminals of the flip-flops 22 and 32resetting them (lines 106 & 118); and to the reset terminal of the BurstPulse Counter 24 resetting it in order that it may count the next trainof pulses emanating from the Threshold Network 16.

The reception by the receiver 10 of the second tone burst, at time stopsthe time interval measurement process. This is accomplished, againbeginning at line 1114, by the reception of the first pulse from theThreshold Network 66 which, again, corresponds to the leading edge ofthe received intentionally transmitted tone burst. The first pulse fromthe Threshold Network 16, at time 11,, line 104, sets the Mono-Controlflip-flop resulting in a logic 0 signal appearing on its output terminal26 and this logic signal is applied to the Process Delay MonostableMultivibrator 78. The application of the logic 0 signal to theMonostable Multivibrator 78 trips it to provide a logic 0 signal (line108) at point 82. The logic 0 signal at point 82, again, has no effecton the Strobe Generator 80 but again, causes the flip-flop 60 to toggleresulting in a logic 0 signal, line 112, to appear on its outputterminal 67 and a logic 1 signal to appear on its output terminal 68.The logic 0 signal on output terminal 67 is applied to input terminal 69of Clock Gate 66 thus disabling Clock Gate 66. Consequently, the ClockGate 66 no longer permits the Clock 76 to supply the clock pulses to theinterval counter 64 (line 114). Thus, the time interval measurementceases.

Also, at time t the recognition measurement process begins again. Thefirst pulse and the succeeding pulses from the Threshold Network 16(line 104, at t are applied to the Burst Pulse Counter 24. If thecounter 24 achieves the predetermined count which can be equated to a 50ms interval, which it again will in the current example as the secondwaveform received is in fact 50 ms in duration, then it providesappropriate output signals to the Decode unit 30 via trunk line 28 tocause the output of the Decode unit 30 to provide a logic 0 signal (line116, at time t,,) to the set or S terminal of the Burst Decisionflip-flop 32. Again, there has been a verification that an intentionallytransmitted tone burst has been received. A logic 0 signal on the Sterminal of flip-flop 32 will cause it to set resulting in a logic 1signal (line 118, at time to appear on its output terminal 38 and alogic 0 signal to appear on its output terminal 34. in this condition,the flip-flop 32 applies a logic 2 signal to the input terminal 40 ofTransfer Gate 42 and a logic 0 signal to the input terminal 36 of ResetGate 1. Again, these later two gates are not enabled at this time due tothe logic 0 signal appearing on the input terminal 36 of AND Reset GateI and due to the logic 0 signal appearing on the output terminal STB-lof Strobe Generator 80 which is applied to input terminal 96 of theTransfer Gate 42. It will be noted, however, that at time t the TransferGate 42 has two logic 1 signals applied to its input terminals; one dueto the logic 1 signal now appearing on terminal 68 of flip-flop 6t) andalso appearing on input terminal 72 and the other appearing on its inputterminal 40 due to the logic 1 signal appearing on output terminal 38 offlip flop 32.

At time t,;, line 108, the Process Delay Monostable Multivibrator 78times out resulting in a logic 1 signal appearing at point 82. Thetransition of the Monostable Multivibrator 78 from a logic 0 level to alogic 1 level again causes the Strobe Generator 80 to provide a logic 1signal (line 120) on its output terminal STE-1. This logic 1 signal isapplied to the input terminal 56 of Reset Gate 1 with no effect on ResetGate I due to the logic 0 signal appearing on the input terminal 36 ofReset Gate 1. It is also applied to the input terminal 90 of TransferGate 42, and, because of the logic 1 signals appearing on the other twoinput terminals of Transfer Gate 42, it passes through the Transfer Gate42 resulting in a logic 1 signal appearing on the output terminal 44 ofthe Transfer Gate 62 (line 130) at time i The logic 1 signal appearingon output terminal 44 of Transfer Gate 42 also appears on the inputterminal 46 of the Storage Register & Readout Display device resultingin the transfer of time interval information thereto via trunk line 98from the interval Counter 6d. The Storage Register and Readout Displaydevice 50 will indicate either the time in milliseconds between theleading edges of the received intentionally transmitted tone bursts orprovide directly an indication of the number of such burst per minutethat are received.

From the foregoing it will be understood that the receiver 10, and inparticular the Display Device of the Storage Register & Readout Displaydevice 50, will provide information to an observer indicative of theoutput pulse repetition rate of a cardiac pacer when intentionallytransmitted tone burst signals representing these pacer output signalsare received thereby.

At time line 122, a second strobe pulse or logic 1 signal is againgenerated by the Strobe Generator 80 and appears at its output terminalSTE-2. This logic 1 signal is applied to the reset terminal of flip-flop32 causing its output terminal 38 to revert to a logic 0 level (line118) and it is applied to flip-flop 22 causing its output terminal 26 torevert to a logic 1 (line 106). The logic 1 signal on terminal STE-2 isalso applied to the input terminal 92 of AND Reset Gate II, and, becausethe other input terminal 70 of Reset Gate II has applied thereto a logic1 signal from output terminal 68 of flipflop 60, the strobe pulse passesthrough reset gate ll resulting in a logic 1 signal appearing on itsoutput terminal 65. The logic 1 signal on output terminal is applied toinput terminal 63 of the OR gate thus enabling the OR gate and resultingin a logic 1 signal to appear on its output terminal 62 (line 128) whichin turn results in the Interval Counter 64 having a reset signal orlogic 1 signal applied to the reset terminal thereof. The IntervalCounter is thus ready to begin the tine interval measurement processanew upon the reception of the next received signal. It will be notedthat from after time 1,, until the reception of the next signal at timethe conditions that existed at time t with respect to the variousoutputs of the various components of the receiver Ill.

Considering now Case B of FIG. 2, wherein an initial noise pulse isreceived by the receiver 16 at time and beginning at line 1 with thetrain of pulses from the Threshold Network 16, the first pulse therefromsimultaneously begins the time interval measurement process and therecognition measurement process as in case A with the reception of thefirst tone burst signal. However, the count in the Burst Pulse Counter24 never reaches the preprogrammed count as the noise signal is in factno 50 ms in duration. Accordingly, no decode signal is ever provided toset the Burst Decision flip-flop 32 as is indicated by the dashedindications at time lines 116 and 118. in this situation, the outputterminal 38 and the output terminal 34 of flip-flop 32 are,respectively, at logic 0 level (lines 118) and logic 1 level. Thisresults in a logic 0 signal being applied to the input terminal as ofTransfer Gate 42 and a logic 1 signal being applied to the inputterminal of Reset Gate I. Consequently, at time t when the Process DelayMonostable Multivibrator 78 times out (lines 1418) resulting in theStrobe Generator providing the logic 1 signal on its STB-l outputterminal (line 126), the Transfer Gate 432 blocks the first strobesignal from passing therethrough and, therefore, time intervalinformation is not transferred from the time Interval Counter 64 to theStorage Register & Readout Device. The first strobe signal does,however, pass through the Reset Gate I as the input terminal 36 thereofhas applied thereto a logic 1 signal from the output terminal 34 of theflip-flop 32. The strobe pulse passing through Reset Gate 1 results in alogical 1 signal appearing on its output terminal 52; line 124 at time tWith a logic 1 signal appearing on output terminal 52., the inputterminal 56 of the OR gate also has a logic 1 signal applied theretoresulting in a logic 1 signal (line 128, at time appearing on the outputterminal of the OR gate which resets the Interval Counter. The timeinterval measurement process is thus aborted. The logic 1 signalappearing on output terminal 52 is also applied to reset terminal R ofthe flip-flop 60 resetting the same and resulting in the output terminal67 thereof to revert to a logic level; line 112 at t This has the effectof isolating the IOKI-Iz Pulse Oscillator 76 from the interval counter.It can be seen what has taken place so far in case B in no way hasaffected the information contained in the Storage Register and ReadoutDisplay device 50 and that no ambigious readings have resulted by thereception of the noise signal.

At time t line 122, the second strobe pulse is generated by the StrobeGenerator 80 resulting in alogic 1 signal appearing at its outputterminal STB-2. This results in the Burst Pulse Counter 24 being resetand the flip-flop 22 resetting and reverting to the state wherein alogic 1 signal (line 106) appears on its output terminal 26. Also, thelogic 1 signal appearing on the output terminal STB-Z appears at the Rterminal of the flip-flop 32 but has no effect as the flip-flop 32 wasnever set, and it also appears at the input terminal 92 of AND ResetGate II and passes through the Reset Gate II. In passing through ResetGate H, it ultimately passes through the OR GATE (line 128) to the resetterminal of the Interval Counter 64, however, it has no effect in thatthe Interval Counter has already been reset. The functioning of the ORgate in this latter situation is merely redundant. The receiver aftertime t again is at the conditions with respect to the various outputsthereof, as at time t Considering now Case C of FIG. 2 wherein the firstsignal is an intentionally transmitted signal which is followed by anoise pulse, the operation of the receiver 10, upon the reception of thefirst tone burst at time is the same as in Case A upon the reception ofthe first tone burst at time t Upon the reception of the noise pulse attime t the operation of the receiver is essentially the same as in CaseB upon the reception of the noise pulse at time t Although the operationof the receiver 10 has not been set forth in detail in Case C, the stepsare shown in the timing diagram and may be readily understood withreference to the detailed explanation of the steps of operation of thereceiver 10 set forth in Cases A and B.

From the foregoing, it will be understood that the described receiver 10continually sifts through all received signals to find two successiveintentionally transmitted tone burst signals without any interveningnoise from which to derive a valid time interval measurement. Statedanother way, the implementation of the receiver 10 described is suchthat valid time interval information is derived between the leadingedges of the first and second tone burst signal; between the leadingedges of the third and fourth, etc. Valid time interval informationcould easily be derived from between the trailing edges or from betweenthe first and second tone burst, the second and third tone burst, thethird and fourth tone burst, etc. In the latter situation, however, theactual implementation of the receiver would be more complex and costly.

It should also be understood that each of the components shown in blockform in FIG. 1 can be readily implemented with commercially availablemicrocircuit components. Further, while the description of theimplementation of the receiver 10 has been presented in terms of AND-ORlogic, the receiver 10 can easily be implemented or converted to NAND-NOR logic circuit elements which are most readily availablecomercially. The con-version can be easily accomplished through.standard techniques of logic circuit design. Thus, one can form thelogical AND function with two NAND gates.

Examples of the components illustrated in FIG. 1 are set forth in thetable below:

Circuit Commercial Type Amplifier l4 Fairchild Semiconductor 741operational amplifier Texas Instrument Inc.

Schmitt Trigger, SN 7413 Fairchild Semiconductor 9601 RetriggerableMonostable Multivibrator Threshold Network 16 Process Delay MonostableMultivibrator Decode Counters Luminetics Corp. 5916 Decade Driver withMemory Luminetics Corp. series 20 Accutronics Inc. KK-82-28P StorageRegister Readout Display 50 IOKl-lz Pulse Oscillator Having thusdescribed our invention, we claim:

1. Receiver apparatus adapted to have coupled thereto successive signalseach being characterized as having a predetermined number of pulsationsand, at times, noise signals comprising:

a. first means for measuring the time interval between successivesignals coupled to the receiver, and

b. signal verification means for verifying that each signal coupled tothe receiver is either a signal having a predetermined number ofpulsations or a noise signal and for aborting measurements of the firstmeans when a noise signal is coupled to the receiver.

2. Receiver apparatus as defined in claim I wherein the first meansincludes:

a. pulse generating means for providing a continuous pulsating signal ata preselected frequency, and

b. counter for counting the continuous pulsations of the pulsegenerating means.

3. Receiver apparatus as defined in claim 2 wherein the signalverification means is operable in response to each signal being coupledto the receiver for verifying that each signal coupled to the receiveris either a signal having a predetermined number of pulsations or anoise signal, and for stopping the operation and resetting the counterwhen a noise signal is coupled to the receiver.

4. Receiver apparatus as defined in claim 3 including means operable inresponse to successive signals being coupled to the receiver toalternately start and, unless the operation of the counter is stoppedand reset by the signal verification means, to stop the counting of thecontinuous pulsations of the pulse generating means whereby the countregistered in the counter between each starting and each stopping of thecounter not effected by the signal verification means is indicative ofthe time interval between each two successive signals having apredetermined number of pulsations coupled to the receiver.

5. Receiver apparatus as defined in claim 4 including a. display means,and

b. means controlled by the signal verification means for effecting thetransfer to the display means of the count registered in the counterbetween each starting and each stopping of the counter not effected bythe signal verification means whereby to provide to an observerinformation indicative of the time interval between each two successivesignals having a predetermined number of pulsations coupled to thereceiver.

6. A receiver apparatus adapted to have coupled thereto signals whichare transmitted over a communication link, the signals includingintentionally transmitted signals of preselected frequency and durationand, at times, noise signals which are introduced into the communicationlink, and being constructed and arranged to continually sift through allreceived signals coupled thereto to locate each two successiveintentionally transmitted signals without any intervening noise signalstherebetween for providing information indicative of the time intervalbetween each such two successive intentionally transmitted signals, thereceiver apparatus comprising:

a. means for providing a continuous pulsating signal at a preselectedfrequency,

b. a digital counter for counting the pulsations of the pulsatingsignal,

c. signal verification means operable in response to each signal beingcoupled to the receiver for verifying that each coupled signal is eitheran intentionally transmitted signal or a noise signal, and for stoppingthe operation and resetting the counter when a noise signal has beencoupled to the receiver, and

means operable in response to successive signals being coupled to thereceiver to alternately start and, unless the operation of the counteris stopped and reset by the signal verification means, to stop thecounting of the pulsations of the pulsating signal whereby the countregistered in the counter between each starting and each stopping of thecounter not effected by the signal verification means is indicative ofthe time interval between each two successive intentionally transmittedsignals coupled to the receiver.

7. A receiver as defined in claim 6 wherein the signal gfiifii' sfiiiiiiii'viii' iieans for converting each signal coupled to the receiverinto a standardized train of pulses, each train of pulses substantiallycorresponding in time duration to the duration, in time, of each signalcoupled to the receiver, and

b. a second digital counter operatively connected to the thresholdnetwork for counting the pulses of each standardized train of pulses.

8. A receiver as defined in claim 7 including means controlled by thesecond digital counter for resetting the first named counter if apredetermined number of pulses in a train of pulses are not counted bythe second digital counter and for inhibiting the resetting of the firstnamed counter if a predetermined number of puises in a train of pulsesare counted by the second digital counter.

9. Receiver apparatus as defined in claim 6 includmg:

a. display means, and

b. means controlled by the signal verification means for effecting thetransfer to the display means of the count registered in the counterbetween each starting and each stopping of the counter not effected bythe signal verification means whereby to provide to an observerinformation indicative of the time interval between each two successiveintentionally transmitted signals coupled to the receiver.

1. Receiver apparatus adapted to have coupled thereto successive signalseach being characterized as having a predetermined number of pulsationsand, at times, noise signals comprising: a. first means for measuringthe time interval between successive signals coupled to the receiver,and b. signal verification means for verifying that each signal coupledto the receiver is either a signal having a predetermined number ofpulsations or a noise signal and for aborting measurements of the firstmeans when a noise signal is coupled to the receiver.
 2. Receiverapparatus as defined in claim 1 wherein the first means includes: a.pulse generating means for providing a continuous pulsating signal at apreselected frequency, and b. counter for counting the continuouspulsations of the pulse generating means.
 3. Receiver apparatus asdefined in claim 2 wherein the signal verification means is operable inresponse to each signal being coupled to the receiver for verifying thateach signal coupled to the receiver is either a signal having apredetermined number of pulsations or a noise signal, and for stoppingthe operation and resetting the counter when a noise signal is coupledto the receiver.
 4. Receiver apparatus as defined in claim 3 includingmeans operable in response to successive signals being coupled to thereceiver to alternately start and, unless the operation of the counteris stopped and reset by the signal verification means, to stop thecounting of the continuous pulsations of the pulse generating meanswhereby the count registered in the counter between each starting andeach stopping of the counter not effected by the signal verificationmeans is indicative of the time interval between each two successivesignals havIng a predetermined number of pulsations coupled to thereceiver.
 5. Receiver apparatus as defined in claim 4 including a.display means, and b. means controlled by the signal verification meansfor effecting the transfer to the display means of the count registeredin the counter between each starting and each stopping of the counternot effected by the signal verification means whereby to provide to anobserver information indicative of the time interval between each twosuccessive signals having a predetermined number of pulsations coupledto the receiver.
 6. A receiver apparatus adapted to have coupled theretosignals which are transmitted over a communication link, the signalsincluding intentionally transmitted signals of preselected frequency andduration and, at times, noise signals which are introduced into thecommunication link, and being constructed and arranged to continuallysift through all received signals coupled thereto to locate each twosuccessive intentionally transmitted signals without any interveningnoise signals therebetween for providing information indicative of thetime interval between each such two successive intentionally transmittedsignals, the receiver apparatus comprising: a. means for providing acontinuous pulsating signal at a preselected frequency, b. a digitalcounter for counting the pulsations of the pulsating signal, c. signalverification means operable in response to each signal being coupled tothe receiver for verifying that each coupled signal is either anintentionally transmitted signal or a noise signal, and for stopping theoperation and resetting the counter when a noise signal has been coupledto the receiver, and d. means operable in response to successive signalsbeing coupled to the receiver to alternately start and, unless theoperation of the counter is stopped and reset by the signal verificationmeans, to stop the counting of the pulsations of the pulsating signalwhereby the count registered in the counter between each starting andeach stopping of the counter not effected by the signal verificationmeans is indicative of the time interval between each two successiveintentionally transmitted signals coupled to the receiver.
 7. A receiveras defined in claim 6 wherein the signal verification means includes: a.threshold network means for converting each signal coupled to thereceiver into a standardized train of pulses, each train of pulsessubstantially corresponding in time duration to the duration, in time,of each signal coupled to the receiver, and b. a second digital counteroperatively connected to the threshold network for counting the pulsesof each standardized train of pulses.
 8. A receiver as defined in claim7 including means controlled by the second digital counter for resettingthe first named counter if a predetermined number of pulses in a trainof pulses are not counted by the second digital counter and forinhibiting the resetting of the first named counter if a predeterminednumber of pulses in a train of pulses are counted by the second digitalcounter.
 9. Receiver apparatus as defined in claim 6 including: a.display means, and b. means controlled by the signal verification meansfor effecting the transfer to the display means of the count registeredin the counter between each starting and each stopping of the counternot effected by the signal verification means whereby to provide to anobserver information indicative of the time interval between each twosuccessive intentionally transmitted signals coupled to the receiver.